U.S. patent number 4,071,689 [Application Number 05/727,153] was granted by the patent office on 1978-01-31 for lucent electrographic sensor for determining planar coordinates.
This patent grant is currently assigned to Elographics, Incorporated. Invention is credited to L. Dexter Bates, John E. Talmage.
United States Patent |
4,071,689 |
Talmage , et al. |
January 31, 1978 |
Lucent electrographic sensor for determining planar coordinates
Abstract
An electrographic sensor for determining planar coordinates is
described whereby graphical material to be analyzed may be placed
beneath, or projected against, the rear surface of the sensor. This
sensor is of particular value for placing on the face of a cathode
ray tube. The sensor includes a rigid, optically transparent
substrate having an extremely uniform, substantially transparent
resistive layer applied to one surface, small electrodes in contact
with the resistive layer and individual resistors connected between
adjacent electrodes to produce a resistance network around the
perimeter of the substrate. Means are provided to produce
orthogonal electrical fields in the resistive layer whereby the
contacting of the resistive layer with a conductive stylus produces
voltage signals at the stylus which are proportional to the
coordinates of the point of contact. The second surface of the
substrate may be made translucent for projecting optical images
thereagainst.
Inventors: |
Talmage; John E. (Oak Ridge,
TN), Bates; L. Dexter (Oak Ridge, TN) |
Assignee: |
Elographics, Incorporated (Oak
Ridge, TN)
|
Family
ID: |
24921537 |
Appl.
No.: |
05/727,153 |
Filed: |
September 27, 1976 |
Current U.S.
Class: |
178/18.09 |
Current CPC
Class: |
G06F
3/045 (20130101) |
Current International
Class: |
G06F
3/033 (20060101); G08C 021/00 () |
Field of
Search: |
;178/18,19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robinson; Thomas A.
Attorney, Agent or Firm: Skinner; Martin J.
Claims
We claim:
1. A lucent electrographic sensor for use in determining x- and
y-coordinates of a point, which comprises:
a rigid sheet of transparent substrate;
a substantially transparent, chemically stable uninterrupted
resistive layer of a semiconducting metal oxide adherently
deposited on one face of the substrate in an amount to produce a
sheet resistivity of a selected value in the range of about 100 to
3000 ohms per square;
corner spot electrodes in each corner of the sensor in electrical
contact with the resistive layer;
a plurality of spaced-apart edge spot electrodes along each edge of
the sensor in electrical contact with the resistive layer;
a plurality of discrete first resistors connected between adjacent
of all of the edge spot electrodes; and
a plurality of discrete second resistors connected between the
corner spot electrodes and adjacent edge spot electrodes whereby
the first and second resistors form series resistor networks along
each edge of the sensor.
2. The sensor of claim 1 wherein the substrate is glass and the
resistive layer has a variation in uniformity of about .+-.1%.
3. The sensor of claim 2 wherein the resistive layer has a sheet
resistivity in the range of 100-500 ohms per square.
4. The sensor of claim 3 wherein the resistive layer is a deposited
oxide of metals selected from the group comprising tantalum,
indium, tin, antimony and mixtures thereof.
5. The sensor of claim 1 wherein each of the edge and corner spot
electrodes is small with respect to the spacing therebetween;
wherein the edge spot electrodes along each edge of the sensor are
equally spaced from each other electrode along that edge and from
the adjacent corner spot electrodes; wherein all of the first
resistors are of equal resistance value; and wherein all of the
second resistors are equal and each have a resistance value greater
than the value of each of the first resistors.
6. The sensor of claim 5 wherein the corner and edge spot
electrodes are circular and their diameter is about 1/64 inch; the
spacing therebetween is from about 1 inch to about 2 inches; the
resistive layer is indium oxide having a selected sheet resistivity
in the range of 100 to 200 ohms per square; the first resistors are
each of a value of about 4 ohms with a precision of at least 1.0
percent; and second resistors are each about 5 ohms with a
precision of at least 1.0 percent.
7. The sensor of claim 5 wherein each of the edge spot electrodes
is individually displaced toward the center of the resistive layer,
from lines joining the corner spot electrodes, an effective
distance such that application of an electrical potential across
the resistive layer by opposite pairs of the series resistor
networks produces equal potential lines substantially parallel to
the lines joining the corner spot electrodes whenever the
equipotential lines are at least one spot electrode separation
distance from the most inwardly displaced edge spot electrode.
Description
BACKGROUND OF THE INVENTION
Our invention relates generally to a system for graphical data
interpretation, storage, transmission and the like, and more
particularly to an electrographic sensor which may be placed over
graphical data to be analyzed or have the graphical data optically
projected against the rear surface of the sensor. The term
"graphical data" as used herein, is any source of information
presentable in two dimensions. In addition, the term "lucent" is
defined to cover all transparencies from clear to translucent (see
Webster's Dictionary). The term "processed," as used in conjunction
with data, is intended to cover interpretation, storage,
transmission and the like.
Considerable effort has been expended in recent years toward
apparatus for graphical data processing. Many of the devices
developed for this purpose utilize orthogonal electrical fields in
a sensor unit together with a probe that is movable across the
sensor to derive a signal proportional to the position of the
probe. These signals may be in analog or digital form. The most
pertinent prior art known to us are the devices described in U.S.
Pat. No. 3,632,874 issued to Lucien C. Malavard on Jan. 4, 1972,
and U.S. Pat. No. 3,798,370 issued to George S. Hurst on Mar. 19,
1974.
The patent to Hurst teaches a construction of an electrographic
sensor whereby very accurate position-related signals can be
obtained. This involves the use of spot electrodes along the edge
of an opaque resistive paper in the sensor, and discrete resistors
connected between adjacent electrodes to form resistor networks
across which voltages are applied to produce uniform orthogonal
electric fields. However, the structure can only be used to process
data placed on top of the sensor. This prevents its use in such
applications as those associated with cathode ray display tubes or
optical projection from the rear of any sort.
In the patent to Malavard, one embodiment is described for copying
graphical data. He specifically mentions cathode ray display tubes.
No teaching is given in the patent, however, as to the composition
of the "thin conduction layer" applied to the "substrate." Whatever
the composition, the transparency of the sensor is reduced
substantially according to his admission. Also, Malavard does not
teach how he would produce the terminals along the edge of the
unit. Furthermore, he teaches the use of a graphite stylus to
contact the sensor. We know from previous experience that this is
damaging to surfaces and causes a relatively short sensor
lifetime.
Accordingly, no suitable transparent and highly accurate
electrographic sensor was known in the art. Furthermore, no sensor
was known whereby projected images of data could be processed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a simplified circuit that is
substantially equivalent to that found in the above-referenced U.S.
Pat. No. 3,798,370 for the purpose of permitting a description
herein of our invention;
FIG. 2 is an enlarged cross sectional drawing illustrating our
improved electrographic sensor; and
FIG. 3 is a drawing illustrating the preferred location of the
electrodes shown in FIG. 1.
SUMMARY OF THE INVENTION
Our electrographic sensor comprises a rigid sheet of an optically
transparent substrate having applied to one surface thereof a
substantially transparent, stable, adherent abrasion-resistant
layer having a uniform sheet resistivity of about 100-3000 ohms per
square, and a resistor network along each edge of the substrate in
contact with the resistive layer at specific positions. These
resistor networks may be produced using a plurality of small
electrodes spaced along the edges of the substrate in contact with
the resistive layer and individual resistors connected between
adjacent electrodes as taught in the Hurst patent. The substrate is
mounted within a suitable frame, and circuitry is utilized to apply
voltages to the resistor networks in a manner to produce orthogonal
electric fields in the resistive layer. A nonabrasive conductive
member, used to contact the resistive layer at desired data
positions, is connected to the circuitry whereby voltage signals
are produced that relate to the position of contact of the member
on the sensor. The conductive member may be, for example, a
stylus-type probe having a conductive core and an insulating shell.
If desired, the opposite surface of the substrate may be frosted or
etched to permit projecting images thereagainst.
In a preferred embodiment, the substrate is glass and the resistive
layer is a very uniform deposit of a semiconducting metal
oxide.
DETAILED DESCRIPTION
Our invention may best be understood by reference to FIG. 2. A
glass plate 10 has a durable (e.g., adherent and chemically-stable)
resistive layer 11 permanently applied to one surface thereof,
referred to hereinafter as the sensor face. A highly uniform sheet
resistance of this layer of a selected value in the range of about
100-3000 ohms per square is suitable; however, a uniform selected
resistivity in the range of 100-500 ohms per square is preferred.
The resistive layer 11 must be substantially transparent, i.e.,
have a transparency of at least 60% and preferably 90% of the
transparent substrate. A layer having these characteristics can be
produced by the deposition of various semiconducting metal oxides,
such as indium oxide or indiumtin oxide, upon the glass sheet. A
product of this type may be obtained, for example, from Optical
Coating Laboratory, 2798 Geffen Ave., Santa Rosa, Ca. This product
(LC-4004 Rev. C "Transparent Indium Oxide") is marketed in sheets
1/16 to 1/4 in. (0.16 to 0.635 cm) thick and, for example, 11.5 in.
wide and 16 in. long (approx. 30 .times. 40 cm) with a coated area
of 10.8 .times. 16 inches (27.4 .times. 40 cm). An area of about
8.5 .times. 11 inches (approx. 22 .times. 28 cm) has a very uniform
(.+-.1%) resistivity of about 100 ohms per square.
Although the transparent substrate of our sensor has been glass in
the above-stated description, other transparent substrate materials
may be used. For example, a suitable resistive layer may be applied
to sheet forms of acrylic plastic and the like.
Near the edge of the glass 10, but in contact with the resistive
layer 11, are a plurality of spot electrodes 12. These electrodes
12 are typically 1/32 to 1/8 in. (0.08 - 0.32 cm) in diameter and
spaced apart about 1 to 2 inches (2.5 - 5.0 cm) (see FIG. 1). A
conductive paint may be applied with a screen or mask to produce
these electrodes on the resistive layer. Uniform spacing between
the spot electrodes is most convenient and is perferred. Connected
between adjacent electrodes are resistors 13 to form resistor
networks along each edge of the glass 10 as taught in the Hurst
patent. The values of the resistors are determined by the
resistivity of the layer on the glass. In general, their value is
about 1/100 to 1/20 of the resistivity; e.g., 5 ohms for 100 ohm
per square of the resistive layer. A precision of at least 1% is
preferred.
The glass is mounted in a suitable frame 14 whereby the electrodes
12 and the resistors 13 are protected but the major portion of the
glass 10 is exposed on both surfaces, i.e., the sensor face 11 and
a rear surface 15. This rear surface 15 may be untreated, for
example, or etched to produce a screen upon which images may be
projected from slides or other optical systems. The glass 10 may be
held in frame 14 with an insert 16 around the perimeter.
Also shown in this figure is a probe 17 for use in the contacting
of the resistive layer 11. This probe has a conductive core 18 so
that the resistive layer may be electrically connected to voltage
measuring circuits (not shown) for purposes described
hereinafter.
It will be understood that the resistor networks along each edge of
the resistive layer may be produced by means other than the spot
electrodes and individual resistors. A typical alternative is the
deposition of areas of resistive material having a substantially
lower resistance than that of the resistive layer. For example, a
ribbon of gold may be vapor deposited to provide the desired
results.
In still another embodiment, the glass with its resistive layer is
removable from the resistor network. This is accomplished, for
example, by placing the spot electrodes (spot conductive regions)
on the resistive layer as above-described. The resistors, in turn,
would be joined to contacts at positions corresponding to
anticipated positions of the spot electrodes. Physical union of the
spot electrodes and the contacts then provides the resistor network
connections whereby the necessary orthogonal electrical fields may
be applied to the resistive layer.
While various materials may be deposited on the glass to achieve a
desired resistivity, indium oxide appears to be highly suitable for
the application of our sensor. For example, gold may be
vapor-deposited upon the glass; however, it is not abrasion
resistant and would have short life as a sensor. Similarly, a
graphite layer would not be abrasion resistant. In contrast, a
chromium layer is hard and will not scratch. It does, however,
oxidize readily and prevents the ready attachment of electrodes. In
addition to indium oxide, a uniformly deposited layer of tantalum,
tin, antimony (as oxides) or a combined layer of indium oxide and
tin oxide can be produced with suitable characteristics for our
sensor. Other similar resistive layers that are adherent,
chemically stable, and provide a resistance in the range of about
100-3000 ohms per square without excessive reduction in
transparency, are suitable for our sensor. In general,
nonstoichiometric oxides of metals in Groups III and IV, with metal
impurities from adjoining Groups of the Periodic Table of Elements,
are suitable.
The nature of the resistive layer, e.g., vapor-deposited indium
oxide, on the glass necessitates the use of a nonmarking and
nonabrasive conductive probe or stylus 17. We have found that the
conductive portion 18 of the stylus 17 may be "Ecco-Shield SV,"
marketed by Emerson & Cuming, Inc., Canton, Mass. Other
potential materials are conductive elastomers and conductive
plastics such as those described in Modern Plastics, Mar. 1976, p.
36-41. One such material is marketed by Technical Wire Products,
Inc., Cranford, N.Y. None of these materials mark the resistive
layer and are substantially nonabrasive.
The manner of using our sensor of FIG. 2 is illustrated in FIG. 1.
This figure is similar to FIGS. 1 and 4 of the above-cited patent
to Hurst. The resistive layer 11 and spot electrodes 12 are
illustrated. The corner electrodes are identified as A, B, C, and D
for reference purposes hereinafter. Two types of resistors are
used: resistors 13 of one value (about 5 ohms) join the corner
electrodes A-D to adjacent electrodes; and resistors 19 (only two
are shown along an edge for illustration purposes) of a second
value (about 4 ohms) are connected between other electrodes 12
along each edge. The total resistors along each edge form resistor
networks 20 (from A to D), 21 (from A to B), 22 (from B to C) and
23 (from C to D).
Two solid state switches 24, 25 are used to apply a voltage from
source 26 in an orthogonal manner to the resistive layer 11. When
switches 24, 25 are moved to contacts X, X', respectively, both
ends of resistor network 21 are connected to the negative terminal
of source 26 via leads 27, 28 while both ends of resistor network
23 are connected to the positive terminal thereof by leads 29, 30.
The resistors of networks 20 and 22 then act as voltage dividers to
produce uniform equipotential lines with a gradient in the
x-direction. In a mutually exclusive time period, switches 24, 25
are moved to positions y, y' by a signal on leads 31-33 from
oscillator 34. In this position of the switches, all electrodes
along resistor network 20 are at a negative potential via leads 27,
35 and all electrodes along resistor network 22 are at a positive
potential via leads 29, 30, and 36. During this interval, resistor
networks 21, 23 act as voltage dividers to assure a uniform
potential gradient in the y-direction.
Since the resistive layer 11 is very uniform and the resistors 13,
19 are very precise, the voltage at any point, P, on the resistive
layer is proportional to the x- and y-coordinates of P. Therefore,
the conductive core 18 of probe 17 in contact with the resistive
layer 11 at point P will convey a voltage to an analog-to-digital
convertor (ADC) and storage system 37 through flexible electrical
lead 38. The coordinates of point P, in the form of voltages, may
be uniquely distinguished (x versus y) by the system due to the
lead 39 between the oscillator 34 and the ADC-Storage unit 37 as
the signal thereon distinguishes the position of the switches 24,
25.
The stylus 17 may be moved at any desired rate across the resistive
layer 11 giving rise to time-separated x- and y-coordinate
proportional signals. If the data is to be scanned slowly, the
oscillator 34 is operated at a frequency of a few Hertz. At higher
frequencies, up to about 1 kHz, the stylus may be moved at a more
rapid rate. This will permit, for example, curve following,
signature-producing signals, etc.
As stated above, all spot electrodes connected to a resistor
network having both ends thereof connected to the same voltage
source terminal have substantially the same potential. The only
deviation is caused by a flow of current through resistors 13, 19,
for example, due to the potential across resistive layer 11. Exact
potentials are required for most applications of the embodiment;
therefore, corrections can be made by relocating the edge spot
electrodes as shown in FIG. 3. The edge spot electrodes are
displaced toward the center of layer 11 a distance, d, so as to
compensate for the above-described voltage drop through the
resistors. Thus, electrode 12 is displaced from a line between
corners A and D a distance to overcome the drop through resistor
13, and electrode 12' is farther displaced to overcome the drop
through resistors 13 and 19 in series. The displacement distance is
thus greatest (d.sub.max.) for edge electrodes farthest from a
corner electrode.
The effective displacement distance is such that application of a
potential across the resistive layer, through the use of the
opposite pairs of resistor networks, produces an equipotential line
which is substantially parallel to the line joining the corner spot
electrodes when the equipotential line is at least one spot
separation, s, from the most inwardly displaced electrode, i.e.,
12' in FIG. 3. The value of d for each edge electrode is determined
from the approximate equation: d = (.DELTA.V/V)L, where .DELTA.V is
the potential drop measured from a corner spot electrode to the
particular edge spot electrodes; V is the potential across the
entire resistive layer, and L is the distance between oppositely
disposed rows of spot electrodes on the sensor.
The principal value of our sensor is being able to place the sensor
over graphical information, such as displayed on the face of a
cathode ray tube, and through the action of tracing the information
with the stylus, convert the data into electrical signals for
storage, computation and the like type of data processing. The data
being traced also may be that on prepared "hard copy" material that
is placed beneath the transparent sensor. Even information of fixed
objects may be processed by taking the sensor to the object.
Some other types of data may be processed which cannot be processed
by sensors of the prior art. For example, data on sheets larger
than the sensor may be processed through the use of optical
reduction equipment and the projection of the reduced image against
the back of the sensor. For this application, of course, the rear
surface is made into a "screen" by frosting, etching, etc.
Likewise, small pieces of data may be enlarged and projected
against the sensor rear surface to permit data processing.
As stipulated above, one of the most advantageous applications of
our sensor is in conjunction with oscilloscopes. The sensor may be
used in a manner similar to the use of a "light pen". Data
displayed upon the face of the cathode ray tube of the oscilloscope
is traced or otherwise processed through the use of our sensor and
the information transmitted to a computer for a variety of
purposes. If desired, this information may be fed back into the
oscilloscope in order to modify the data. However, in contrast to
the light pen, which only interacts through an area of light on the
cathode ray tube, contact of the stylus on our sensor may be made
at any point and the information used to interact with the data.
This permits the insertion of hard copy data beneath the sensor and
thus the rapid inputting of ancillary data into the computer. Due
to the transparency of our sensor, the conventional light pen may
also be used, if desired.
The above-described uses of our sensor are given only for
illustration and are not intended to limit the applicability of the
sensor. Many users will, undoubtedly, recognize applications where
our lucent electrographic sensor will uniquely provide for data
processing.
* * * * *